A majority of steel stator cores used for production of automotive alternators, such as shown in FIGS. 1 and 4 at 10 are produced using a well-established process called helical winding (albeit with some variations) such as shown at 11 in FIG. 3, that involves the following basic steps:                1) Slitting a thin width coil, typically 20 mm to 70 mm in width, from a wide coil of electrical steel where the thickness is typically 0.50 mm but which may vary from 0.35 to 1.00 mm.        2) Stamping with a stamping die 2 the slit coil 1 as shown in FIG. 2 to create two separate continuous strips 12 and 13 that are interlaced, but which are separated like a zipper. Some processes stamp and separate up to 4 continuous strips, wherein two opposing strips are interlaced and the boundary in the center between the two pairs of interlaced strips is straight. Each strip is comprised of a straight support section 12A (called the “back-iron”) from which protrude teeth 12B which may be straight or look like “T” sections attached to the back-iron. The teeth end faces 12G have a slight concavity or curvature substantially matching a rotor peripheral curvature. Gaps 12C between the teeth are known as “slots” (see FIGS. 2 and 3). Indentations 3 are provided opposite the base of each tooth in the back-iron.        3) Winding each of the continuous strips, such as onto a central mandrel, such that each strip forms a helix 11 (with turns separated as shown in FIG. 3) which forms the helical core 10 (FIGS. 1 and 4), similar in concept to a child's toy popularly known as a “Slinky”. After winding to a fixed core height (or mass), the continuous strip is cut, leaving an individual helical core 10.        4) Clamping and welding at for example separated locations 9 (FIGS. 1 and 4) around a periphery of the helical wound core to form the solid core 10 (FIG. 4).        5) Coining of the welded helical wound core to ensure consistent dimensions for the slot 12C openings and to impart any additional features on the faces of the core or on the edges leading into the slots.        6) A specially designed copper wire winding 14 (FIG. 1) is then inserted into the slots 12C (FIG. 4) of the finished helical wound core 10 to form the stator section of the alternator.        
Over the last 15 years, the quality of steel used to manufacture alternator cores has improved from 1.00 mm commercial quality grades to the current use of 0.50 mm fully processed electrical steel, typically grades with core loss maximums of 8.00 watts/kg @1.5 Tesla, 50 Hz. Other grades and thicknesses are in use. The driving force for the reduction in steel thickness and the improvement in electrical properties is the increasing requirement for higher current output and higher efficiencies from automobiles that have an increasing requirement to support an increased number of electrical devices. However, the demand for higher output from the same weight and package size continues.
A normal approach taken by automotive manufacturers and Tier 1 suppliers for an increase in current output and efficiency is to increase the diameter and/or the core height of the helical wound core. Another option is to increase the number of slots in the helical wound core which allows a more efficient design of copper winding to be inserted. However, there is a limit as to how much weight can be added by increasing the mass of the alternator core. There is also a limit as to how many slots can be added to a core since there needs to be a balance between wire diameter, number of turns and the amount of steel used in the teeth of the core to establish sufficient electrical flux. So both of these design options appear, to those skilled in this art, to have reached limits, which do not seem to those skilled in this art to readily provide further options for increased current output. As indicated, some manufacturers have also used thinner electrical steels e.g. 0.35 mm, to reduce electrical losses and thereby increase current output. One of the problems with this approach is that the costs for manufacture of a helical wound core are inversely proportional to the thickness of the steel used. The reality is that the mechanics for successfully winding a helical core without crinkling the flat steel becomes much more difficult as the steel becomes thinner.
The difficulty in using the thinner electrical steel described above can best be understood by reference to FIGS. 5A and 5B. In FIG. 5A a first prior art method for helically winding a strip 12 is illustrated. An inside pressure wheel 8 is provided which contacts an outer edge 12G of the teeth 12B and exerts a force thereon. Also an outer pressure wheel 7 is provided which abuts against an outer edge 12F of the back-iron 12A of the strip 12. The strip is thus bent, resulting in internal plastic deformation in both the teeth 12B and within the back-iron 12A of strip 12. Inside pressure wheel 8 may also be a mandrel or have an associated mandrel about which the strip is helically wound.
A second prior art method is shown in FIG. 5B which is known from U.S. Pat. No. 7,797,977. Here an outside pressure wheel 4 is provided along with a partial cone-shaped inside pressure wheel 5 having notches 5A. The notches 5A receive a base portion of the teeth 12B. A separate mandrel 6 is also provided to receive the helically bent strip. In this method the teeth 12B are not stressed by the bending (but are stressed by stamping) and plastic deformation still occurs in the back-iron 12A which is subjected to bending pressure by the inside pressure wheel 5 on the inner edge 12E of the back-iron 12A and pressure is also applied by the outside pressure wheel 4 on the outside edge 12F of the back-iron 12A. Thus plastic deformation occurs within the back-iron.
At present, only three companies in the world are known to be successfully winding helical cores with a steel thickness of 0.35 mm and no one is winding cores using thinner steel. So, while the demand for increased alternator output continues, the opportunity to obtain increased output using thinner electrical steels has appeared to be limited to 0.35 mm for both commercial and mechanical reasons.
Some manufacturers have examined the use of higher grade fully processed electrical steels. In theory, the lower electrical losses of these grades of steels, (especially at higher frequencies such as 200 to 600 Hz, which is the major part of the operating conditions for the alternator) should result in an increased current output. However, there is an anomaly, which is not understood by most manufacturers, such that the use of higher grades of electrical steel result in alternator performance that is either the same or not as good as alternator performance using regular grades with core loss maximums of 8.00 watts/kg @1.5 Tesla, 60 Hz. So again, while the demand for increased alternator output continues, the opportunity to obtain increased output using higher grade electrical steels has appeared, to those skilled in this art, to be limited.